wtdash Posted June 11, 2012 Share Posted June 11, 2012 2004 Forester XT 180K - NEWLY rebuilt engine, w/new CTS (water temp), plugs, wires, new front AFR / O2 sensor... When cold, car runs poorly - stumbles and hesitates for 1st 1-2 minutes 'til it warms up. No CEL. It's worse w/colder weather we've had the the last week - mid 30's F. It did this BEFORE the Rebuild and After. And it does it on the Stock tune, a Cobb OTS tune, and a Custom -online- tune. Leads me to believe it's an 'Open Loop' issue in the ECU's programming? The front O2 sensor is new - Not the rear, but since they're not used until it gets to Closed Loop, they shouldn't matter? I'm not sure what to log on the Cobb AP but guessing that's a place to start. Thanks for any feedback. Td Link to comment Share on other sites More sharing options...
Fairtax4me Posted June 14, 2012 Share Posted June 14, 2012 Vacuum leak? PCV and breather hoses connected tightly? Seems like it should be something basic. Checked timing belt alignment? Link to comment Share on other sites More sharing options...
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